There is NO rule that says your lather, after only one application, must remain moist and shaveable throughout an entire shave, and there is NO shame in relathering areas that are drying out. I think some people figure that with a nice brush and a good soap you will get some magical lather that never dries out. This is simply not the case. Often technique is blamed for lather drying out; sometimes this is true, especially if your lather is gone within a couple minutes. Usually environmental factors are at play - dry air, water quality etc. If you find your lather is drying up on certain areas of the face just take the 10 seconds and "freshen" it up a bit and you're good to go.