"Constant vigilance" means continually being on watch or guard against threat. This is a phrase used by the kooky one-eyed auror, Alastor "Mad-Eye" Moody, in J.K. Rowling's Harry Potter book series. The character was introduced in the fourth book of the series, Harry Potter and the Goblet of Fire.
Here, constant vigilance means being continually aware of areas that need improvement. For me, I am constantly searching for valuable resources to ensure I am able to solve any problem that comes my way. The ultimate goal is a repertoire of languages, paradigms, skills, and experiences sufficient to solve the biggest problems in human health.