How do hydraulic flat tappet lifters fail?

While we’re here, can I make a pitch for solid flat tappet and adjustable rockers. You need a cam/lifters and some of your rockers need attention or replacement. What you really don’t want is to replace the cam/lifters and it survives the break in, but it starts to collapse a lifter at moderate rpm. This will cost more for new rockers, but you will not have to worry about a lifter collapsing or pumping up. The maintenance on a solid lifter is over stated. Once they settle in they don’t change much. Check them once a year. Think of it like a physical for your engine. Also for a somewhat inexperienced person, you become more comfortable working on it and if the lash starts to open up, you might stop a small issue from turning into a big issue. Just my 2 cents.