A pop-up that breaks someone's flow costs trust. Save it for decisions that cannot be undone.
Unsolicited modals break flow and erode trust. Reserve them for irreversible decisions.
An unsolicited modal hijacks attention. Prefer an inline banner, and save the hard stop for irreversible actions.
Prefer inline banners or tooltips. Give modals one primary action and an obvious dismiss.
You're three lines into an article when a full-screen “Subscribe” modal covers it. You didn't ask for it, it blocks the thing you came for, and your first instinct is to hunt for the close button. That interruption costs attention and goodwill. Compare a quiet inline banner that waits at the end of the piece: same offer, no hijack. Save the hard stop of a modal for the rare moment that genuinely needs one, like confirming you're about to delete something.
A modal is the right tool when the decision really is blocking or irreversible: confirming a delete, a payment, or the loss of unsaved work. There the interruption is the point, forcing a conscious choice before something can't be undone. The rule is against unsolicited interruptions, not against ever stopping the user.
An AI coding copilot fires a suggestion modal, a 'tip', and an upsell the moment you start typing. It breaks flow so often that developers reflexively dismiss everything — including the suggestions that would have helped.
Users ignore alerts because an automated system produces too many low-quality warnings.
An AI meeting assistant pops suggestions and summaries mid-conversation, breaking everyone's focus.