Bash. As an intermediate programmer, I learned it too late. Scripts were always magic to me since I was used to compiled languages. Especially useful for certai

Bash. As an intermediate programmer, I learned it too late. Scripts were always magic to me since I was used to compiled languages. Especially useful for certain build tools and manual steps programmers are running from the command line. Personal financial tracking - budgeting and tracking everything in Mint or YNAB. Going from "I spend about this much total money per month" to "I spend this month in each of these categories" was big as far as having confidence in my finances. Similarly, setting up a retirement account. You should do this as soon as you're over 18 and have a full-time job, no matter whether your salary is low.