Tlalocan is the paradise of water and green growth, and admission to it depends entirely on the manner of death. Drowning, lightning strike, and diseases understood as sent by Tlaloc, dropsy and gout among them, all qualified. Those who died these ways were buried rather than cremated, which was the normal treatment, and the change in rite is the clearest evidence that the doctrine was acted on and not merely stated.
The best-known image of it is a mural at Tepantitla in Teotihuacan, showing small figures playing, swimming, singing with speech scrolls, and moving among streams and flowering plants, beneath a large central figure. Alfonso Caso identified the scene as Tlalocan and the reading became standard. It has been challenged since, notably by Esther Pasztory, who argued the presiding figure is a goddess rather than Tlaloc, and the identification is now treated as probable rather than settled.
The doctrine is worth holding onto because of what it implies. A cosmology in which the manner of your death, and not your conduct, decides where you go is describing a world governed by which power claimed you. Being struck by lightning is not misfortune in that frame. It is selection.