While we are prone to regret inaction, there is rarely a valid objective reason for such regrets. Even if we fail to take action, and the opportunities that are associated with that action are gone forever, this does not mean that we are doomed to the then-current state of affairs. As Richard Branson pointed out, opportunities are like buses, because there is always another one coming.
If we fail to act on a particular opportunity, a constructive lesson from that experience is that we are learning to recognize the opportunities and the moments when resistance, so vividly described by Richard Pressfield in “The War of Art”, sneaks in and keeps us from doing the work. For example, when I am shooting with a lens that works alright for the particular situation, i.e. it has an adequate focal length and f-number, I need to consciously make myself stop shooting and change to a different focal length (taking action) to avoid falling into a complacent shooting mode. Varying the gear, camera settings, subjects, composition, etc. might seem like a hassle at the time, but it is almost always worth it in retrospect. The good news is that that it is never too late to try all these new things at the next photo shoot, even if I miss the opportunity on a particular day.