Shantideva goes on to say:

(8.92) The suffering I experience
Does not harm others,
But I find it hard to bear
Because I cherish myself.

(8.93) Likewise, the suffering of others
Does not harm me,
But, if I cherish others,
I shall find their suffering hard to bear.

This is a very clever line of reasoning.  To understand it, we need to make a clear distinction between “being harmed” and “finding something unbearable.”  Sometimes people think compassion means we are equally harmed by the suffering of others, and to find their suffering unbearable means we find it equally painful.  If this was the case, who would ever want to generate compassion since it would be a cause of infinite suffering.  Surely it would be better to remain in different to the suffering of others than to experience all suffering.  Therefore, making this distinction is crucial.

From a conventional point of view, if I break my arm, it harms me and not others.  If find this harm both painful and unbearable.  It is painful because it was my arm that was broken.  It is unbearable because I cherish my own happiness and well-being as being important.  It is perfectly possible for me to find this experience painful (since it is my arm that was broken), but perfectly bearable because I don’t consider my well-being to be particularly important. 

Now imagine somebody else breaks their arm.  From a conventionally point of view, this does not harm me, but it does harm others.  It is harmful to them because it is painful to them.  Their pain is not my pain.  Their pain does not harm me.  Everyone knows this.  If I do not care about their well-being, then their pain will also be perfectly bearable for me.  It is not my problem.  For them, however, this experience is definitely painful because it is their arm that is broken.  It may or may not be bearable for them depending on whether they cherish themselves or not.  If I do care about their well-being, and I consider it to be important, then their pain will not be harmful to me, but it will be unbearable. 

Pain, or harm, is a function of whether we are imputing our I onto an aggregate of feeling of something that is harmed.  Bearability is function of whether we consider the happiness and well-being of that person to be important. 

But unbearability does not necessarily mean we suffer from it.  Whether we suffer from the unbearability of other’s suffering depends upon whether we have attachment to others well being or whether we are free from such attachment.  To be attached to others’ well-being means we think our own happiness depends upon them not suffering.  That’s what attachment to anything means – we think our happiness depends upon some external factor.  If we have attachment to this person not suffering, their breaking their arm will be both unbearable to us AND it will be experienced by us as suffering.

Therefore, for compassion – finding others suffering to be unbearable – to NOT be suffering for us, our mind must be free from attachment to other people suffering.  If we have attachment, we will suffer from their suffering.  If our mind is free from such attachment, we will still find their suffering unbearable (because we consider their happiness and well being to be important), but we won’t experience that unbearability as suffering.  How will we experience it, then?  To be unbearable means we can’t just sit there and do nothing about it.  We feel compelled to do something because it is unbearable. 

This is where our wisdom comes in.  What do we feel compelled to do?  If we lack wisdom, we might get mad at the other person for whatever it is they did to break their arm, hoping that our anger will deter them from making similar mistakes again in the future.  Maybe that will help, but most likely not.  But what will help?  Us becoming a Buddha.  If we become a Buddha, then we can gradually help others change the basis of imputation of their I onto an enlightened being whose arms never break.  We see the only lasting solution to their suffering is for them to attain liberation and enlightenment themselves.  How can we bring that about?  By we ourselves first attaining enlightenment for their benefit – we attain enlightenment with the express purpose of being able to in the future lead these people to freedom.  The strong feeling of unbearability, that is free from attachment to them not suffering, and that possesses the wisdom that actually knows what is beneficial to others is the pure mind of compassion that is the substantial cause of a qualified bodhichitta.  This unbearability will push us to become a Buddha.  If we have attachment or we lack wisdom knowing what can actually help, this unbearability could lead to ourself suffering at best and us feeling the need to control others at worst. 

The key here is understanding we don’t have to be harmed by suffering to find suffering unbearable. We are harmed by suffering, we find suffering then unbearable, but we do not have to be harmed by suffering in order to find suffering unbearable.  If we have wisdom and are free from attachment to others not suffering, finding the suffering of others unbearable naturally leads to love, compassion and virtuous actions, which creates the causes for our future happiness. 

But what do we do about our own suffering?  We may still be harmed because we are in samsara, but if we do not cherish ourself at all, then we will find the suffering we experience to be entirely bearable.  It will not be important, just as the suffering of others is unimportant to us now.  Indeed, when we let go of thinking that our own experience is important, we find whatever pain we are experiencing to be eminently more bearable, and this creates the space within our mind to actually be able to transform our suffering into something useful for the spiritual path.  Then, not only will it be bearable, we will start to understand Shantideva when he says “suffering has many good qualities.”  For us, it will still be painful, but so beneficial.  Then, others suffering will not be our problem.  Our suffering won’t be our problem.  Others’ suffering will be a cause of our enlightenment.  Our suffering will be a cause of our enlightenment.  Perfect!

But if we cherish only others, won’t we suffer from the suffering of everybody?  No, because we do not experience their suffering.  So by cherishing others, we do not experience their suffering, but we find it unbearable and so we are lead into spiriutal paths.  And by not cherishing ourselves, we find our own suffering entirely bearable, so it is not a problem for us at all.  In short, we put our cherishing where it can’t be harmed – others.  Shantideva’s wisdom is unparalleled.