There is always a time for high risk/high reward, it's why people play decks like oops and belcher. It's always possible to win/lose to a nut draw though, that's part of the game. By the same token sometimes hands can line up perfectly. Knowledge of the format is the best answer in the end. You need to know where choke points are and find a way to leverage them to your advantage. Keeping risky hands can be fine, sometimes it's just how you play it out. Simply consider these 3 cards: land tax, mox diamond, plains. When and how you play those cards can have huge ramifications right from turn 1. Play just the plains? Mox into tax? Just the mox? Sandbag for a turn? Etc. We walk a line where ultimately we want to force our opponent to play our game and those turn 1 plays can set the tone.