If you haven’t had a good night’s sleep, you know why you’re being a bit slow; but if you observe someone else being slow you don’t have such knowledge and so you might presume them to just be a slow person. Because of this disparity in knowledge we often overemphasize the influence of circumstance for our own failings, as well as underestimating circumstantial factors to explain other people’s problems.
It’s not only kind to view others’ situations with charity, it’s more objective too. Be mindful to also err on the side of taking personal responsibility rather than justifying and blaming.