This is the 915th most frequent Japanese word.
甘い
Sweet.
In this sentence, '甘い' describes the sweet taste of the cake, demonstrating its basic meaning relating to flavor.
このケーキはとても甘いです。
This cake is very sweet.
In this context, '甘い' expresses naive optimism or lack of thorough consideration, suggesting the idea might not be well thought out.
その考えは甘いと思う。
I think that idea is overly optimistic.
'甘い' here conveys the sense of being lenient or indulgent, indicating a forgiving or non-strict behavior.