Thousands of years ago, when the Greek philosophers were laying the first foundations of geometry, someone was experimenting with triangles.
They bisected two of the angles and noticed that the
angle bisectors crossed.
They drew the third bisector and surprised to find that it too went through the same point. They must have thought
this was just a coincidence.
But when they drew any triangle they discovered that the
angle bisectorsalways intersect at a single point!
This must be the 'center' of the triangle. Or so they thought.
After some experimenting they found other surprising things. For example the
of a triangle also pass through a single point (the orthocenter).
But not the same point as before. Another center! Then they found that the
medians pass through yet another single point.
Unlike, say a circle, the triangle obviously has more than one 'center'.