You HAVE to remember to clean your knife and cutting board after chopping garlic and onions.
Normally in the kitchen you become so occupied with prep that you forget onions and garlic can carry over their flavors long after you've finished dicing and slicing. If you don't believe me, then do this.
Chop some garlic and then dice up an onion. Wait about 5-10 minutes, and then cut into a fresh apple or juicy watermelon.
Does anything taste "funny" to you?