Flush draws are tricky: The best case scenario is you have the A, and 2 of the flush cards, while the flop has 2. If this is the case, you have 36% chance to win a flush. This is because there are 9 cards of the flush left potentially to draw, and each card is about 2% of the deck, so 9 X 2% X 2 cards left to draw = 36% chance to get there. If you have the K, not the A, getting the flush doesn't necesarily win the hand. Your 36 % just got reduced by 4% (the odds the A could be in someone elses hand. You have to multiply that 4% subtraction for each person still in the pot with you, so if 2 villains are in the pot, then subtract 8% from 36%).
If you only have 1 of the flush cards, and 3 are in the flop, then it is more likely someone else will have a flush too, because now they only need 1 to begin with rather than 2 assuming one more comes out on the turn or river. Not as good of a place as the first scenario.
In addition to the K getting outdrawn by the A, you need to have community cards that do not support a full house. If you see a pair in the table, you could be getting set by a full house.