I wore only Crocs last year and didn't have a problem whatsoever. However, the Crocs were new, so the tread was still there. I loved wearing them because they dried out quickly so I didn't have to worry about my feet being wet. As eebadeeba pointed out, when the tread is worn, it can be slippery on wet surfaces...I noticed it slippery on very smooth surfaces such as tile. Otherwise, I don't really have a problem.