I have found, in my own spiritual life, that the more rules I lay down for myself, the more sins I commit. The habit of regular morning and evening prayer is one which is indispensable to a believer’s life, but the prescribing of the length of prayer, and the constrained remembrance of so many persons and subjects, may gender unto bondage, and strangle prayer rather than assist it.

Charles Spurgeon, in Wycliffe Handbook of Preaching & Preachers, W. Wiersbe, p. 235