Faith that w/stands the test of time

Why do some people hold fast to God and others reject Him while still others have some sort of half-hearted commitment to their faith?
Being hurt by Christians, by life, or simply being disappointed by not ideal circumstances can turn us away, as can being constantly exposed to ideas that are anti-God and Christianity. An unwillingness to dig for ourselves into God's way and God's Word certainly erodes the ground of faith.
Jesus's parable of the sower explains that some hearts are simply hard so that the birds can carry the seeds away as they've not sunk in, perhaps because the truth was mixed w/ falsehood and becuase this world so harshly attacked. Some seed is accepted but other concerns of life--interests, goals, desires--more important to someone than God's truth choke it out. But there are those who grow, who truly welcome the seed, the sun, the water, have roots that go down deep and true and drink health and strength and thrive through difficulty to bear lasting fruit.