I've conducted about 100 technical interviews over the past 6 months for a software development recruiting company called Triplebyte. I've also been doing consulting work, which has required me to take numerous technical interviews. It's interesting contrasting the experiences to identify what works and what doesn't.

Every Triplebyte interview begins with the candidate coding a short game. We have a series of steps, and each step precisely defines simple requirements for the program to handle. I can generally tell a couple minutes into the 2 hour interview whether the candidate will be successful. There are certainly outliers (as well as mechanisms to prevent bias), but in general, I can quickly ascertain how well a candidate stacks up technically. So then, it begs the question, why is it so hard to hire engineers? The answer is, most of us are doing it wrong.