Does everything happen as God designed it or is it all by coincidence?

Answer:

Neither. God has a design and purpose which He carries out in the world. "In Him also we have obtained an inheritance, being predestined according to the purpose of Him who works all things according to the counsel of His will" (Ephesians 1:11). God manipulates everything that happens toward the accomplishment of His purpose. "Declaring the end from the beginning, and from ancient times things that are not yet done, saying, 'My counsel shall stand, and I will do all My pleasure,' calling a bird of prey from the east, the man who executes My counsel, from a far country. Indeed I have spoken it; I will also bring it to pass. I have purposed it; I will also do it" (Isaiah 46:10-11).

But this does not rule out that some things happen which have no impact on God's ultimate goals. Thus God may not decide what needs to happen but allows things to happen as they may. "I returned and saw under the sun that - the race is not to the swift, nor the battle to the strong, nor bread to the wise, nor riches to men of understanding, nor favor to men of skill; but time and chance happen to them all" (Ecclesiastes 9:11). Thus we learn that some events occur by simple random chance.

"And we know that all things work together for good to those who love God, to those who are the called according to His purpose" (Romans 8:28). What kind of things does Paul have in mind? "Who shall separate us from the love of Christ? Shall tribulation, or distress, or persecution, or famine, or nakedness, or peril, or sword?" (Romans 8:35). Therefore, God can take even the evil things that may come upon His children and manipulate them such that ultimately it works in favor of His people. It doesn't mean God's people never suffers. Quite the opposite actually. But we know that the suffering is temporary and will ultimately lead to something better.