What does the quote by William shakespeare It is bright day that brings forth adder and craves wary walking mean?

The quote by William Shakespeare from King Lear (Act I, scene 4) means that it is during the bright day that adders (a type of snake) come out, so one must be cautious and walk carefully to avoid them. In other words, even seemingly harmless times can carry hidden dangers, and one must exercise care and vigilance accordingly.