Screws and nails into end grain, never. That is super weak.

Glue into end grain... not recommended by master carpenters I guess but for holding a jig together it's fine. Especially if it's a short fat piece of wood like a chunk of 2x4. I've done it before, and when the glue cures, it's near enough unbreakable. It's not "super super weak" like you were saying... you're thinking of screws into end grain.

I hadn't bothered googling it, was just talking from experience, but since you rudely called me a googler I went ahead and found this video. https://www.youtube.com/watch?v=m7HxBa9WVis It shows that you can break the end-grain glue up at the glue joint, BUT it takes more force to break the glue joint than it does to break the wood on a side-glued joint. So I was partially wrong, the glue will break before the wood if you glue end grain to end, but it is still super strong.