Faith can fluctuate. There are choices you can make to lose it, and there are choices you can make to increase it.
Gaining faith happens internally. Faith happens in you, not to you. It happens in your mind and in your heart, as you introspect and pay attention to what you think and what you feel and why. It happens as you act on what you already know. It happens as you change your desires and augment your reasons.
You lose faith by refusing to act when given sufficient reason to. You gain faith by acting when given sufficient reason to. Faith increases as you seek God and as you reconcile yourself to what he teaches you:
Nevertheless they did fast and pray oft, and did wax stronger and stronger in their humility, and firmer and firmer in the faith of Christ, unto the filling their souls with joy and consolation, yea, even to the purifying and the sanctification of their hearts, which sanctification cometh because of their yielding their hearts unto God. (Helaman 3:35)
Calling on God as you contend with the challenge of reconciling to what you know is a sign of faith, and will bring more faith, so long as you are sincere.
Calling on God without an intent to change and without sincerity will not help you build faith. When a father pled with Jesus to help his son, Jesus said, “If thou canst believe, all things are possible to him that believeth.” (Mark 9:23) The man didn’t have sufficient faith, but he used what he had to implore the Lord for help:
And straightway the father of the child cried out, and said with tears, Lord, I believe; help thou mine unbelief. (Mark 9:24)
The father did not delay—he asked straightway. He did not weakly request—he cried out. He was not limply emotionless—he said it with tears. You lose faith by ignoring opportunities to learn more about reality. You gain faith by making the most of every opportunity to understand more about reality. Rather than thinking of faith as a gift from God, think of it as a matched gift. You can’t beg God for faith and expect him to magically give you more without your contribution.
Success in life is not a function of your ability to beg God. A successful business person is not just another homeless person who happened to beg more or make a more convincing sign to hold up. He found the rules of the game, and he played the game better than those who were less successful. If you want success in life, you will obtain it in the same way. You will discover the rules God lives by, and you will choose to live by them. The more effort you put into discovering the rules, and the more closely you obey them, the more you will progress towards being all that God is and, because of that, having all that he has.
An ancient military leader wrote about how he gained faith in his challenges through calling upon God:
10 Therefore we did pour out our souls in prayer to God, that he would strengthen us and deliver us out of the hands of our enemies, yea, and also give us strength that we might retain our cities, and our lands, and our possessions, for the support of our people.
11 Yea, and it came to pass that the Lord our God did visit us with assurances that he would deliver us; yea, insomuch that he did speak peace to our souls, and did grant unto us great faith, and did cause us that we should hope for our deliverance in him. 13 And thus we did go forth with all our might... (Alma 58)
This man was praying in belief with great effort and the intent to act accordingly. He wasn’t begging God to magically change outcomes. He was praying for confidence to act and wisdom in knowing how to act. He was asking God to magnify his own willing contribution.
You lose faith by intentionally acting contrary to the best you know how. You gain faith by acting in the best way you know. Faith will not increase against your will. To increase in faith, you have to start by doing what you already know.
When a group of prisoners were enshrouded in supernatural darkness, they cried out in horror, presuming they didn’t know what to do about it. One of their fellow prisoners reminded them that three missionaries had already taught them what they should do:
40 And it came to pass that the Lamanites said unto him: What shall we do, that this cloud of darkness may be removed from overshadowing us?
41 And Aminadab said unto them: You must repent, and cry unto the voice, even until ye shall have faith in Christ, who was taught unto you by Alma, and Amulek, and Zeezrom; and when ye shall do this, the cloud of darkness shall be removed from overshadowing you. (Helaman 5)
Faith exists by degrees. Only those who develop great faith will encounter all outcomes available to us in this life and beyond.