What angle would you get at the end of two arcs drawn in the following fashion:
With P as centre and any radius, draw an arc as shown, which cuts in A. This is the first arc. With A as centre and the same radius, cut this arc in B. This would be the second arc.
Since we draw all these arcs with the same radius, it follows that PA = PB = AB. Hence △ ABP is equilateral and hence ∠ BPA = 60∘.