The retrospective is the meeting most likely to skip when the week is hard, and most likely to fix the reason it was hard. Pick a format that matches the conversation you actually need.
Retrospectives are the meeting where a team converts experience into adjustment. They're the only routine slot most teams have where the agenda is 'how are we doing this' instead of 'what are we doing.' The format isn't decorative — different formats produce different conversations. Start/Stop/Continue produces commitments. 4Ls produces understanding. Sailboat produces system-level diagnosis. Five Whys and Fishbone aren't retros at all — they're techniques you run inside one. Pick the one that matches the question you need to answer, and rotate to surface what the regular format misses.
End of every sprint, end of every project, after a release that didn't go to plan, when somebody on the team says 'we should talk about how this is going.' The cadence matters less than the rule that you actually run them — the teams that skip retros when the week is hard are the teams that need them most. Skip the formal retro for one-off meetings or short status calls (use Plus/Delta instead) and skip the big four-quadrant variants for a routine sprint where SSC will do the job in twenty minutes.
Three simple buckets that surface what to begin, end, and keep doing.
A reflective four-column retro for end-of-project lessons.
A four-quadrant retro for naming structural friction without pointing at a person.
Mad first or you wasted the meeting. Glad-first is hosting; Mad-first is working.
SSC with the edge filed off. Run it when 'Stop' feels confrontational and 'Less' feels survivable.
The four-column variant that splits Keep from Improve. Improve is where the work hides.
The retrospective for when you have more topics than time. The timer is the format.
The format you run when 'Mad' is too sharp for the room. Engineering teams should pick something else.
Sailboat is Speedboat with a wind column. Run Sailboat unless you specifically want anchors-only.
A technique inside a retro, not a retrospective on its own. Twenty minutes on one specific incident.
End-of-quarter, end-of-project. The mood line is the format. Don't run it on a sprint.
Two columns is too few. If you want a retrospective, use Start/Stop/Continue. If you want a journal, use this.
Five Whys gives you a chain. Fishbone gives you a map. Software bugs almost always need the map.