Most relationship communication issues start with very small things that build up over time. She secretly hates it when he squeezes the toothpaste tube from the middle instead of the bottom. He is irritated by noisy dishwashing while he’s trying to relax after work.
If you let little annoyances build up without talking through them, communication will start to break down. Then, the small stuff that wasn’t such a big deal initially can snowball into bigger stuff.