Lego wasn’t the inventor of today ubiquitous plastic building blocks - it was a clone of the original called Kiddicraft.

Phil Edwards:

The first Lego plastic mold was the same one that Kiddicraft used, and early Lego bricks were almost identical to Kiddicraft blocks, with a few minor differences. They slightly changed the scale and the studs, but as you can see, they were pretty similar. Early Kiddicraft blocks had little slots in the side for windows and other attachments. So did early Lego bricks. From top to bottom, these were very similar to Kiddicraft blocks. So with such a simple idea that had kind of already been done, how did Lego win?

Lego out engineered Kiddicraft - Lego built a better brick.