If you’re tempted to break a rule, convention, default, or best practice (as we all are, from time to time), make sure you understand the spirit behind the rule first. There are often important motivations behind every rule, and you’ll need to take those into account when bending or breaking them.
A great example is the temptation to remove the default outline styles most web browsers apply to focused elements. These outlines are visually distinct, and you may not like the way they look. Removing them may seem like a harmless design decision, but those default styles are there for an important reason. If you don’t know the motivation behind those default style rules, and don’t take the consequences into account when you override them, your choices will have unforeseen consequences for people visiting your site.
There are times when breaking rules is the right decision, but a deep understanding of those rules is required to keep you from making things worse.