Shops will happily sell you a whole batch of tiles, paint, or wood without warning you how it behaves in real life. A color that looks perfect under showroom lighting can look completely different in your house. A tile that feels smooth in the shop becomes dangerously slippery when wet.
Instead of buying everything at once, buy samples first. Test paint on your actual wall, check tiles with water, place lighting samples in your room at night and daytime. Stand on the tile barefoot, walk on it when wet, check reflection and stains.
Testing avoids regret — because returning installed materials is almost impossible. Real renovation wisdom is simple: sample now or suffer later.