Not that I have a deep well of knowledge, but the dumbest mistake I almost made was dumping a batch.
My first batch (kit nut brown) was horrendous for the first few bottles. If I could go back in time I might be able to accurately describe the flavors, but my impressions at the time ranged from "aghckt... what the...?" to "that's the worst f'n thing Ive ever drank."
Fast forward a few weeks... "Hey, that tastes like beer!"
I came this close to dumping a batch that, while not an award winner, was a drinkable 5 gallons that I knew I could improve. Patience is the toughest part of homebrewing. Now I just try to brew too much, it allows for proper aging.