Why can I not create a unique index with more than 3 columns in mySQL table?

Question

What I want to realize is adding a unique index for every column in a table. But when I add more than 3 columns to the index, it will throw the error that

Error: ER_TOO_LONG_KEY: Specified key was too long; max key length is 3072 bytes```.

I create my table through node.js, and the code is

db.query("CREATE TABLE IF NOT EXISTS tasks (name VARCHAR(255), id VARCHAR(255), `group` VARCHAR(255), owner VARCHAR(255), isComplete BOOL)")

and what I do is

db.query("ALTER TABLE tasks ADD UNIQUE INDEX (name, id, `group`, owner, isComplete)")

When I just add 3 columns, like:

db.query("ALTER TABLE `groups` ADD UNIQUE INDEX (id, name, owner)")

it is okay. So why does this happen?