Sublime Text was an excellent stepping stone for me, some years ago. Through Sublime's “Vintage” mode, I was able to dip my toes into the world of vim-style keybindings, slowly getting more comfortable with that way of moving though a document. Through Sublime's very open plug-in system I learned more Python and wrote a couple of plugins that saw surprisingly wide adoption, for as simple as they were. Sublime took all the promises of TextMate and made them cross platform. In Sublime we have a fully customizable editor that does exactly what you need it to do, because you're fully in control of what it does.
Of course, this led me deeper down the rabbit hole, to actual Vim.
In the intervening years, as Sublime Text has moved fairly slowly, other editors have picked up the banner, like GitHub's Atom and, somewhat surprisingly, Microsoft's Visual Studio Code. We now have a plethora of good, simple, intelligent, and most importantly configurable text editors at our disposal, and Sublime has fallen behind. But I will always be grateful for how it led me into a wider, better world of editors.