William Pitt invested much in the battle as he thought that establishing North America was necessary for Great Britain as a world influence. In a different global strategy was applied by William Pitt where he inserted money and supplies in the colonial battles, while the French concentrating more on the fight.
Hence, in the end, it all occurred down to the evidence that the British outnumbered the French. Even though the French did really great with guerilla tactics, it was the important fights that mattered by killing French fighters that were not efficiently replaceable.