cross a bridge before one comes to it

cross a bridge before one comes to it

 and cross that bridge before one comes to it
Fig. to worry excessively about something before it happens. (Note the variations in the examples. See also cross that bridge when one comes to it.) There is no sense in crossing that bridge before you come to it. She's always crossing bridges before coming to them. She needs to learn to relax.
See also: before, bridge, come, cross, one