We are all inconsistent to some extent. It is embarrassing when someone publicly points out a contradiction in our lives. It's harder not to be a hypocrite if what we preach is overly strict obedience to petty rules than if we preach mercy and grace. However, we are expected to have a certain measure of credibility. We can't just talk the talk. We must also walk the walk, albeit imperfectly.
Legalism tends to make us hard on others and soft on ourselves, because we cannot keep all of our petty rules perfectly. It creates hypocrisy, a form of self-deception. Mature Christians acknowledge flaws easily and don't pretend. Their preaching is merciful. The best preaching is open and honest about our own vulnerability. Then we are sincere and not pretenders. We are not play-acting or putting on a phony facade. We are genuine. It's not so hard to practice what we preach if what we preach is grace instead of legalism.