Very good! You had $$10$$ to begin with, you gave away $$4$$. But, obviously, in total, there are still $$10$$ chocolates. So, chocolates only changed hands.
Imagine there are two cars travelling at $$40 \, \mathrm{km/h}$$. They are travelling in opposite directions and unfortunately crash into each other and stop moving. Before they crashed, if you added their speeds, you would get $$40 + 40 = 80 \, \mathrm{km/h}$$.
• It is $$< 80 \, \mathrm{km/h}$$
• It is $$= 80 \, \mathrm{km/h}$$
• It is $$> 80 \, \mathrm{km/h}$$