In a healthy dynamic, safe words during kink play are like referee signals in a football(soccer for Americans) game. I'm going to try and give a (possibly too) thorough explanation here, because I know not everyone is a sports fan.

tl;dr caution words and safe words are useful tools for keeping a scene safe and enjoyable for everyone and not inherently cause for guilt. Major violations usually go beyond safe words and into long-term consequences/re-evaluations.

Caution words are like flags.

You're playing the game, and you kick the ball down field. All of a sudden the assistant referee's goes straight up. This is an indication that no rule has been broken yet, but if the play develops in a certain way, it's going to result in a violation. Most likely offsides. Or you kick the ball out of bounds and the AR points their flag toward your team's end of the pitch. That means it's not your ball anymore.

Generally speaking, when the AR's flag goes up, play continues uninterrupted, but a redirection happens in the moment.

There's nothing wrong with the AR's flag going up. It's just an indication that an infraction (usually minor) has been or is being committed. And, honestly, they usually happen when someone's trying to follow the rules and makes a minor and correctable error. Honestly, a player that never triggers the AR flag is probably playing things too safely... or has an AR who's bad at their job. Depending on the situation, you might personally feel bad about breaking the rule - being a step offsides on a play that could've turned into a goal if you'd remained onside certainly doesn't feel good - but objectively, no serious offense was committed. It's just a thing to be aware of, and adjust play accordingly.

If someone caution words you, they're waving that AR's flag. Depending on the action involved and what you were hoping would develop, you might personally feel bad about the caution being given, but the infraction itself is really not that big a deal so long as you redirect. And the reality is, if a caution word is never triggered, then either the Dominant actually has some unexplored territory to examine, or the submissive is not speaking up enough.

Safe words are like whistles.

When the referee's whistle blows, play stops while the referee sorts out the situation. This is a definite violation of the game's rules, but generally speaking it can be dealt with pretty quickly. The most common violations are, again, things done without the intent of breaking a rule - following through on an offsides play because you didn't see the flag (or saw it but interpreted it incorrectly), or sliding in a little too aggressively, or breaking a rule without really thinking about it. Some players' style is to go hard until they see what triggers a whistle from a given ref. Others try to avoid a whistle at all costs. But so long as they respect the whistle and aren't intentionally breaking rules, it's not a massive deal when they get one.

If someone safe words you, they've blown the whistle. Again, it's entirely reasonable to feel bad. It doesn't feel great to be told you were too rough, or failed to understand your partner's caution signals. But again, the word is there to enable play to continue with some correction and redirection. The only thing you really need to evaluate there is whether the frequency of safe words you get matches up with your intended play style and/or your submissive's comfort level.

In summation, neither caution word nor safe word is necessarily a cause for guilt. They're just how we make sure we're playing correctly.

There Are Further Steps For Serious Infractions

In football, in addition to flags and whistles, there are cards. These are given by the referee after a whistle is blown. A yellow card is the referee saying either you clearly broke a rule on purpose, or you took a clearly unacceptable risk. It's basically "I'm letting you off with a warning this time, but don't try and pull that shit again."

A red card is for when a serious offense is committed and the person who commits it is immediately removed from play. But even in this case one need not always feel bad about it occurring. Players receive red cards if the ball happens to deflect off their hands and the referee determines a goal would otherwise have been scored. It's a valid enforcement of the rule, and also the clear lack of intent on the part of the player being sent off is usually a good basis for their not feeling too much guilt over it.

Further review of a red card violation can also lead to long-term or even permanent bans. These are almost always because the player being suspended either committed a majorly egregious offense, or has a past history of bad behavior.

The same is true in kink play. A safe word is like the whistle - it signals that things need to be stopped until the person giving the signal can issue correction.

But it's what happens next that will indicate the severity of the infraction. It might just be a "hey, don't do that" and play continues.

It might be a "you know that's a no and need to stop pushing it" and play still continues.

It might be a "we're done for now." Sometimes this is because you intentionally crossed a line. Other times it's because you accidentally crossed a line you were aware of. Still other times, it's you and your partner both finding out about a line neither of you previously knew existed.

Or it might be "we're done for a while" or even "we're done forever." But to get to this level, someone will normally have had to fuck up majorly and/or repeatedly.