Never test the depth of water with both feet.
If you’re testing the depth of water with both feet down, you risk being drowned if the water turns out to be deep. But if you test with one foot, you can pull away. The proverb means that before going whole hog into something unknown, assess the risk well.
Example: Before investing such large sum in crypto and taking a hit, I should’ve first invested a small amount or talked to experts. One should never test the depth of water with both feet.