Although, none of us are promised tomorrow, it is still a good idea to have a plan. God has set that example for us. He had a plan for all His children collectively, before He laid the foundations of the earth.
34 “Then the King will say to those on his right, ‘Come, you who are blessed by my Father, inherit the Kingdom prepared for you from the creation of the world.–Matt. 25:34 (NLT)
He also has plans for each of His children individually.
11 For I know the plans I have for you,” says the Lord. “They are plans for good and not for disaster, to give you a future and a hope.–Jeremiah 29:11 (NLT)
So, it is not wrong to have plans. They are only a problem and a boast when we plan without asking God about it. Or if we think that we can accomplish anything good without God. We are only here on this earth for a very small portion of time and then we are gone. So, we need to spend our lives “redeeming the time”, in other words, making good use of it to further the work of the Kingdom of God. This was His plan when He created the world and us.
10 For we are God’s masterpiece. He has created us anew in Christ Jesus, so we can do the good things he planned for us long ago.–Eph. 2:10 (NLT)
So, we see that God planned us, formed us, and then created us anew to do His good works for His glory. If we plan anything less, it does not honor our Creator and if we plan anything greater, it is presumptuous and sinful. When we know to do good and refuse to do it, it is a sin against God and our fellowman.