why i use [0] or [1] to index the number is wrong, why .start and .end is right?

```
intervals = sorted(intervals, key=lambda i: i[0])
rinter = []
for i in range(len(intervals)):
if rinter and intervals[i][0] <= rinter[-1][1]:
rinter[-1][1] = max(intervals[i][1], rinter[-1][1])
else:
rinter.append(intervals[i])
return rinter
```