I hate Minecraft mods. These are additional JARs that you can load into your Minecraft environment to add cool features and new things to play with. As a concept, this is a wonderful thing.
In practice, it is a steaming pile of poo.
The way Minecraft is structured, all of the mods need to be loaded into a single mods directory. But not all of the mods are available for all of the versions of Minecraft. Some of the mods will refuse to run if you don't fire up the correct version of Minecraft and will prevent Minecraft from loading at all. You can flip between versions of Minecraft that you intend to use, which is a wonderful, easy-to-use feature, but pick the wrong version and some mod will shut you down.
And did I mention that all of the mods seem to be hosted on websites that desperately attempt to download malware onto your computer? Or, as I encountered today, give you the "You need to call Microsoft!" screen with a bogus phone number for bogus tech support?
Of course, little girls love mods and beg me to download them. Three out of four times, the mod fails to work after I have run the gauntlet. And then is much sadness and "Can I have a different mod?"
I hate Minecraft for having a design this stupid. I just Googled and there are some marvelously complex ways to try to work around the problem.
But it all falls into the category of "What idiot designed this system?"