I'd say it's actually very hard to find effective charities. Most charities don't evaluate the outcomes versus the cost of their work, regardless of their earnest desire to be helpful. While Charity Navigator and GiveWell can weed out some of the truly bad orgs, the orgs trying to do the right thing and being ineffective is probably a larger problem than anyone realizes. You want to make a huge impact on people's lives? Solve food transportation, early cancer diagnosis, or basic medical care. Those are easily the most impactful and least sexy parts of making lives better.

GiveWell and Charity Navigator are pretty much the opposite. GiveWell has a small list of very thoroughly investigated charities, while Charity Navigator has a big list but doesn't say much of anything about their effectiveness.