When Is It OK to Call a Dive?
The water is glass, the boat is cheerful, and something in your chest is saying no. Five reasons to stay dry — and why the honest answer is: whenever.

You are on a boat. The water is glass. The sky is clean, the breeze is soft, the vibes on the boat are bubbly and cheerful. And something in your chest is telling you no.
Call it trepidation, fear, premonition — better not the last one. If you are reading this, I am going to assume you are a diver. You know your mood can make or break a dive. You also know that a sense of intuition surfaces over time, and you know when to trust it. So — when is it ok to call a dive?
Quick disclaimer. We are talking recreational diving here. Tech diving is a different beast: many of those folks may not get a second chance to dive the Andrea Doria, and they will feel justified splashing in weather that would keep a rec boat tied to the dock.
Back to the question. In recreational diving, when can you call a dive? The answer is banal.
Whenever.
When you did not sleep
This one is common. You have your favorite site in the morning, your mind is racing, you have been charging GoPros all night and prepping memory cards. It happens to all of us.
Yes — being in the water will wake you up. It will also drain you much faster. You are on borrowed time down there, and your performance will be shot. If you have a big dive ahead, the conditions are not ideal, and your head is quietly telling you it is better to stay dry — stay dry.
When the conditions are bad
Heavy swell. Strong current. Terrible viz. A boat crew you do not trust. Dive partners you do not trust. There is zero enjoyment in being thrown around in the swell while you and twenty other divers try to climb back onto a heaving ladder. Panic attacks on the surface are more common than people admit, and they almost always happen in choppy water.
When you do not trust your guide
I am going to be blunt. Most dive "pros" have no business guiding people. In roughly 500 dives I have met at least 50 different guides, and only a handful were competent enough that I would put my beginner friends behind them. I have met guides who were high, guides who were drunk, guides who were aggressive, demeaning, hostile, and — the memorable ones — downright dangerous.
If the communication between you and the guide does not make you feel at ease, relaxed, and safe, ask for a different one. Or skip it. You can talk to the person first — hopefully their ego stays out of the way.
When you just do not feel like it

A quick story. After a painful breakup, I fly back to Phuket to resume my diving. I have been out of the water for two and a half years and I generally feel down. We go to Phi Phi. The first dive is on a site I have never seen before.
I splash. A second later my inflator hose jams and I am stuck at the surface. I signal the guide, kick back to the boat, and spend the rest of the day onboard shooting the islands with my Sony. Everyone asks what happened. The divemaster tries to talk me back into the water. I stay on the boat.
I can always dive another day. I cannot undo an avoidable mistake.
If for whatever reason you do not feel "brave" enough today, do not be a hero. Nobody cares. Stay dry, watch the water, snorkel if you feel like it, have a good day.
When the gear does not feel right

Your trust in your gear is paramount. If you have doubts about a piece of your kit that you have not resolved before the dive, I would not go test it out at 100 feet.
Remember that jammed inflator hose? It stayed harmless because it happened immediately, on the surface, in flat water. Ten metres down, in current, on a wall, that same jam is a different story. DAN's incident data is a small mountain of that difference.
None of this is a licence to bail at the first inconvenience. If you are rested and the conditions are good and the guide is competent and the gear is in order — go. That is what we are here for.
But if any of the above is quietly pulling on your sleeve, do not talk yourself out of it. The best divers I know all call dives.