We usually talk about characters who experienced great opportunities/
Did any character miss any great opportunity that made you sigh and/or weep and/or say "Darn it, you idiot, why didn't you....?"
I'm talking about FORSEEABLE opportunities. Not like "if Ren Woxing would have been born 500 years for Dugu Qiubai to meet" kind of opportunities!
One example is that Lord Long and Lord Mu of Gallant Island could not interpret the secret of Ode to Gallantry art. If they could have concentrated on the right parts of the art, they could possibly have discovered the secret.