ける(かける) (に) To lack an abstract thing (experience / confidence / creativity / trust)
りない(たりない) To not have enough of a physical thing (money, time, a soup needs more garlic). 足りないalso implies that there is a specific amount that is required, which に欠ける does not. Example:I wanted to buy a candy bar but I was 4 yen short (お菓子を買おうとした、4円足りなかった!)