Humans are creatures of the present. Humans have no ability to know the past, they have no ability to know the future. That's why you can't tell what you yourself did today but a year ago.
Science is about a set of rules behind a repeating behavior. Science can be accurate because we have infinitive number of times for us to speculate and observe and predict how this behavior repeats itself in front of us and into the future. We don't fart our satellites randomly in the hope that randomness will bring it to the surface of the moon. Instead it is the law of physics which allows us to predict that we can land on the surface of the moon before we actually launch our rockets. And whenever the mission failed, we won't say that it's mistake of the theory. It's always the fault of human errors, miscalculations, equipment errors, unpredictable factors. The law of physics on the other hand will never be at fault in terms of making such a prediction (a projection into the future). In this case, the law of physics predicts without mistakes. That's what the nature of science is and why it is accurate.
Science however is not an accurate tool to examine a single event in the past or in the future. We don't have any suitable tool for us to do so. It's the lack of suitable means for us to examine into both the past and future, which drives us to employ science to do the job. It's not because science is the suitable it's rather because we don't have any suitable tool at all.
That being said, evolution is assumed to be a repeatable behavior thus we have a valid scientific premise or hypothesis. However evolution (if exists) is a process which takes millions of years to repeat itself. We don't have the time to speculate to observe and to predict infinitive number of times for us to come to a scientific conclusion. We (human scientists) thus gave up the scientific approach to get to a scientific conclusion. What we do is the same as how we employ science to try to examine the past. In this case, science is never a suitable tool, we don't have one at all which drives us to have to employ science to do the unsuitable job.
The Big Bang Theory is in a similar situation. Big Bang can be assumed to be a repeatable behavior, that is, the same Big Bang may occur repeatedly in a multiverse model. However, we don't have the time to speculate, observe, predict infinitive number of times to get to a scientific conclusion. Thus we have to employ science as the unsuitable tool to try to examine into to past.
An analogy is, we identify a qualified pilot by looking into predictably how he can launch and land a plane. We predict that he drives an airplane from the airport of Paris to the airport of New York, and when this prediction comes to pass repeatedly that we can be assured that he's a qualified pilot. This is a result of a repeatable end-to-end speculation, observation and prediction.
The other approach is that we see a human sitting in the cockpit of the plane, we observe his behavior inside the cockpit to come to the conclusion that he's a qualified pilot. This is the approach of evolution (or worse, we examine his fingerprints left inside the cockpit to conclude that he's a qualified pilot).