If P + 1/P < 1, then (P2 + 1) / P < 1
So, (P2 + 1) / P - 1 < 0
(P2-P+1) / P < 0
P2 - P + 1 = P2 - P + 1/4 + 3/4 (by completing the square)
= (P - 1/2)2 + 3/4 > 0 for all real numbers, P
So, since (P2-P+1) / P < 0 and the numerator is always positive, the denominator, P, must be negative.
Therefore, P < 0.