Both involve doing something nobody explicitly assigned you. The difference is almost entirely about whose territory you crossed into, and whether you crossed it with them or around them.
Initiative that gets noticed and rewarded tends to fill a genuine gap, something nobody owns, that's clearly needed, that you're well positioned to do. Initiative that reads as overreach tends to step directly into something someone else already owns, without checking first, even if the intent was purely helpful. The line isn't about how big the action is. It's about whether it required someone else's territory to happen.
Noticing that no one owns the onboarding checklist, and quietly building one that new hires actually find useful, filling a real gap nobody had claimed.
Rewriting a colleague's process document without asking, because you thought your version was better, even if it genuinely was, you've now made a change to something that was theirs, without them in the loop.
The second example might come from a completely good-faith desire to help, but it lands as a boundary crossed, because it happened without the other person's input on something they considered theirs. The exact same improvement, offered instead of imposed, "I noticed a few things in the process doc that might help, want me to share some suggestions?", reads as helpful rather than presumptuous.
The fastest way to turn initiative into a problem is skipping the person whose territory you're about to enter.
A reliable filter before acting on your own initiative: is this genuinely unclaimed, or does it belong to someone, even informally? If it's unclaimed, go ahead, that's exactly the kind of gap-filling that builds a strong reputation. If it belongs to someone, even loosely, a quick heads-up or offer, rather than unilateral action, turns a potential toe-stepping moment into a collaborative one.
One more distinction worth holding onto: initiative on your own work is almost always safe. Initiative that reaches into a team's shared process, a colleague's project, or a decision above your formal authority needs that extra beat of checking first, not because you need permission for everything, but because crossing someone else's territory without a heads-up is what actually damages trust, even when the outcome is good.