Pressed crouch to not fall off platform but fell anyways.

I was trying to make a bridge from my nether portal that is suspended over lava in the air to nearby land. I know of the crouch technique to prevent falling and used it many times, but this one time it didn't work and fell into lava. I was still crouched and no enemies hit me. Lost good gear and a lot of levels. I went back and tried it again and worked.