With the risk of blatantly generalizing, I will blatantly generalize that it hardly speaks well of candidates who, despite all exit polls, quick polls, partial counts, full counts etc counting against them with a wide margin, still declare their victory. It seems unfortunately there has gone quite a bit of inflation in this in recent years: Better to declare yourself a winner, seems to be the logic, as in the short run there is very little to lose, and in the long run, people forget whatever happened in the last election.
Yet this is not a victimless crime: The casualty is the credibility of the electoral institute, whose responsibility it is to name the person who won the most votes, while the electoral tribunal will deal with any potential impugnations and then declare the winner. By having candidates not holding back at all yet bursting out that really, they won, the credibility of these institutions are undermined.
The case in point here is Martha Elena García, the PAN candidate for governor in Nayarit. Despite that all polls - quick counts and I believe exit polls as well - indicated she was behind the winner, PRI's Roberto Sandoval Castañeda, with double digits, she had, mind you, her own poll that showed her ahead by several percentage points. And with this single poll that she claimed to have, she declared herself the winner, suffering ridicule.
AMLO's declaration on the night of July 2-3 2006, though he had promised to await IFE's verdict, is rather tame by comparison.