As an engineer, not knowing how to scale when working on something that may need to scale could spell the downfall of whatever product you're working on. Yes, all is well and fine until you hit a natural growth cycle and can't commission new boxes fast enough because each request is taking 300ms. Your database isn't accepting enough requests (plus, some of your bad queries that aren't indexing are blocking too long). Then your web servers run out of memory because you are using an ORM for large lists of items that you're just returning as an array...

Once you get to the point of no return you have to know what to do or you'll suffer. Learning that when fire is falling from the skies is the worst way in retrospect.