Credit goes to Louis Parkinson in this video for this advice (paraphrased to my understanding):

When projecting, don't treat attempts as if they are worthless, because they aren't. They have a cost. They cost skin, energy, time, motivation, and potentially the patience of spotters/belayers, and all of these are in limited supply. So recognize the value of each attempt and spend them wisely: only make quality attempts. Toward that end, two rules:

  1. Exactly 5 attempts. Fewer than that, and you're maybe giving up too soon, but more than that, and you're achieving diminishing returns.
  2. Don't just jump back on after a failed attempt. Don't get back on until you can answer the questions a) What did I do which caused me to fail? And b) what will I do this time instead?

A few notes: