Scientific explanations
An explanation is scientific when evidence supports it, it can be tested, and it predicts something you can go and check.
A worked example
If 20 of 25 seeds sprout in plain water (80%) and 11 of 25 in salt water (44%), the gap of 36 percentage points is evidence that salt affects germination.
The mistake people actually make
An observation is what you notice; an inference is what you work out from it. When new evidence contradicts an accepted explanation, the explanation is re-examined, not the evidence set aside.