To the Philippians Paul writes: "have no anxiety about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. And the peace of God, which passes all understanding, will keep your hearts and minds in Christ Jesus" (Phil. 4:6-7).
Evidently one sign of deficient prayer is anxiety. As pain tells us of the need for healing, worry tells us of the need for prayer. Prayer functions as a safety valve without which informed Christians would constantly be anxious, aware as they are of the spiritual warfare surrounding them. And since faith is the essential grace expressed by and strengthened through prayer, we might say that we have interceded enough when we have held before God the major responsibilities which confront us and any wider burdens which the Holy Spirit may suggest from day to day, and have exercized faith that he is at work in these.
This is not at all a difficult labor: there may be times when it can be the work of minutes. Too little prayer is an expression of unbelief in God's love and care; so is too much."
- Richard Lovelace in Dynamics of Spiritual Life (p. 160)