There is always the possibility of suffering decompression illness. For amateur divers we think in terms of one bend in every 10,000 or so dives. This does not mean that all dives have an equal chance of a bend occurring one in 10,000 times. Risk increases with depth of the dive, but the relationship is not a simple linear one. The risk of diving to 50m is not five times the risk of diving to 10m, but very much greater.
Diving is like mountaineering.
The top of Everest is some ten times higher than the hills in the Lake District, but the risk of climbing Everest is far more than ten times greater than the risk of a ramble in the Lakes. The risk of climbing increases exponentially with altitude. There are physiological problems such as low partial pressures of oxygen. There is the unexpected avalanche. Mountaineers know that survival involves an element of chance.