I want too much in a deck

Just wondering if anyone has the same problem in building a deck. Basically when building a deck I would focus on putting my goals into the deck, working into it all the possible combination of cards, depending on the strategy I'm going for. But for some reason, my focus goes onto a different focus, like I need something else to combat the opponent. For example, I may build a build a simple elf deck, but realize that I don't have high-powered creatures, or anything to combat fliers, enchantments, etc. So I was wondering if anybody has this same problem with focusing too much into one deck?