Whenever we get blamed, first we have to investigate whether it is deserved or undeserved, because it's probably not useful to us to just ignore every blame that comes to us in our life just by reflecting on our good qualities. If we investigate our intentions and our wisdom level and see whether the blame is deserved or undeserved, if we do find that our intention was good but we lacked some wisdom, then we can try to reflect on our good intentions. This is having sympathetic joy with our good intentions and then try to increase our wisdom. If we investigate and see that we had a good intention and we also had some wisdom, and it is undeserved blame, then reflecting on our good qualities and having joy with them helps us to be less concerned with blame.
If we get a lot of blame and then start doubting about whether we have the capacity to understand, then, yes, having some sympathetic joy is very helpful to reflect on the other side of ourselves. Reflect that we are not just capable of making mistakes but we have also seen times in our practice and in our life where we did do beneficial things and we have this potential within ourselves. Also try not to create jealousy towards other people who may be praised while we are being blamed. Sympathetic joy can help us in our reactions to blame so we are able to have sympathetic joy with our own good qualities realizing that we just made a mistake and have compassionate forgiveness for ourselves and joy with others' good qualities that they are able to understand more deeply than ourselves. Sympathetic joy can be very helpful with dealing with all of the Eight worldly dhammas, blame especially. It can also be helpful with our reactions to praise as well, so that we don't get attached to the pleasant feelings of praise, we can reflect on the qualities that are being praised and realize that we wouldn't get the praise unless these qualities were being manifested. Then try to have sympathetic joy with ourselves and sympathetic joy with the person who is able to recognize these good qualities and praise us. So sympathetic joy is very helpful with our reactions to praise and blame.