I've learned a lot of things from my dad over the years. One of them is that the Bible has many principles in it that God has established and they're working whether or not you believe in the Bible. One thing that God has established in this world is "You have what you say." (Mark 11:23-24) The reason this verse works is because most people believe what they're saying when they say it, without even thinking about it really.
Honestly, I used to think it was weird that my dad applied truth from God's Word to every little thing in life. Now, I see that his faith is real. His faith isn't sunday-only-faith, or believe-what-i-want-when-i-want-faith, but rather faith that lives out God's will in his every day life and TRULY believes all of what God says. The kind of faith God commands us to have. Hebrews 11:1 says "Faith is being sure of what we hope for and certain of what we do not see." If you are sure something is going to happen, your certainty isn't based on faith, it's based on knowledge. The pastor of the church I grew up in defined faith as "believing in the Word of God and acting upon it, regardless of how I feel, knowing that God promises a good result."
Back to the principle - you have what you say. Lots of people are experiencing something in their life - big or small - that is a result of their speech. I used to say "I'm so stressed" a lot. a LOT. (side note: I was one of those people that thought it was somehow impressive to always be stressed or busy, so when people would ask how I was I might respond, "good, but I'm so stressed." or "good, but I'm so busy." Thank GOD I learned to stop doing that. Listen for this in conversations you have with people - it's amazing how many people brag about their busy-ness.) Anyway, guess what. I WAS stressed. I chose stress and I felt stress because I said it a lot. Not once or twice. A lot. Another example, think about someone you know who might be experiencing depression. I am not minimizing the real emotional state that people experience, especially when they don't have the resources to deal with a devastating circumstance or a chemical imbalance... but does this person you know often say (to themselves or others) "I'm so depressed." Definitely not helping their situation. My dad said that when I was 2, everyone would tell him, "oh no! watch out- terrible twos" (or something along those lines). He knew they were just joking, going along with popluar cultural phrase to make conversation, but he would respond "no. she's great. we call them the terrific twos." And sure enough, I guess my two year old phase was great.
A small thing that my longest friends might find humorous. I used to drop my phone a lot. Again, not once or twice, but a lot. I also said "I drop my phone all the time" all the time. I would tell all sorts of people that. I remember my dad saying... well, you have what you say. So I decided I was going to stop saying that. and guess what? I haven't dropped my phone in a long time.
This is one of those principles that is working for or against you whether or not you believe God's Word. Try it. Pick something you say that is negative. Replace it with the positive alternative. See if it impacts you over a period of time. It could be big or small. Maybe a family member that you always speak negatively about is living up to your negative expectations. Maybe a 2-year-old to call "terrific" instead of "terrible." Maybe you talk about how nervous or anxious you feel a lot.
What speech are you going to change?