I was wondering if it's counted as a lie when I change my mind. This has been a problem for me lately. Let's say I tell my wife "I'm having a egg sandwich for lunch" and then make a hamburger, is that lying? If I tell myself that I will not drink coffee ever again and then decide I want to, is that lying?
I'm having a hard time keeping my word, and I realize it will be better if I just say "I plan on" doing this or that instead of saying it as a definite.
One of interesting things that came out of our study of II Corinthians is Paul's discussion of why he had to change his plans that he wrote about in I Corinthians. Plans should be kept when at all possible, but to hold on to plans which are no longer best because of changing circumstances simply out of stubbornness is not sensible either. Paul had every intention of following through with his original plan, but since the writing of the first letter to Corinth, Paul came to realize it wasn't the best plan. See: Changed Plans for a detailed discussion.
For example, I might plan on having an egg-salad sandwich for lunch, right up until the time that I realize that the last egg was used for breakfast. A change in plan to adapt to the change in circumstances is perfectly fine. It is why James warned, "Come now, you who say, "Today or tomorrow we will go to such and such a city, spend a year there, buy and sell, and make a profit"; whereas you do not know what will happen tomorrow. For what is your life? It is even a vapor that appears for a little time and then vanishes away. Instead you ought to say, "If the Lord wills, we shall live and do this or that." But now you boast in your arrogance. All such boasting is evil" (James 4:13-16). We should not make promises based on what we can't control.
Stating a preference is merely that, a preference. If someone was counting on my choice, then I would do all I can to make things work out. If my wife had stated, "I'm hungry for a hamburger. I think I'll eat that last leftover one for lunch," and I said, "No problem. I rather eat an egg-salad sandwich." Then when lunch time roles around, I'm not going to change my mind and eat the hamburger, though I might grab the peanut butter and jelly.
This is why Jesus said to let your "yes be yes and your no, no" in Matthew 5:37. The context is what you tell others so that they are counting on what you said (Matthew 5:33-37).
However, circumstances, such as other people's choices, can make you change your mind, just as God changed His mind about Saul. "And Samuel went no more to see Saul until the day of his death. Nevertheless Samuel mourned for Saul, and the LORD regretted that He had made Saul king over Israel" (I Samuel 15:35). Or consider it this way, where would we be if people could not change their minds about worldliness or the false religion they might have chosen. Repentance is the changing of you mind in a good direction.
It is a good habit to acknowledge that life is uncertain in the things we say. That is why James said to say, "If the Lord wills ..." But such phrasing isn't demanded in every single sentence. Often the context of what we say implies that this is an intention. But if context doesn't make it clear, then we should say it so others know we will do our best within the limits of what we can do.