But what I realized was, if you truly have a deep understanding of something, then you can talk about it all day long. Then you can re-derive everything you need from that understanding. No memorization required. You can get to it from first principles. And every piece of what you know is like a Lego block that just fits in and forms a steel frame. It’s solid.

以下是这段英文内容的语法解析：

句子1：But what I realized was, if you truly have a deep understanding of something, then you can talk about it all day long.

• 结构：复合句，包含主句和条件状语从句。
• 主句：“But what I realized was…” 是主系表结构，“what I realized” 是主语从句，作主语；“was” 是系动词。
• 条件状语从句：“if you truly have a deep understanding of something” 由“if”引导，“have a deep understanding of” 是固定搭配，意为“对……有深刻理解”。
• 主句后续部分：“then you can talk about it all day long” 中，“talk about” 是固定短语，“all day long” 是时间状语。

句子2：Then you can re-derive everything you need from that understanding.

• 结构：简单句。
• “re-derive” 是谓语动词，“re-” 是前缀，表“重新”；“everything you need” 是宾语，其中“you need” 是定语从句，修饰“everything”；“from that understanding” 是介词短语作状语。

句子3：No memorization required.

• 结构：省略句，完整形式为“No memorization is required.”，是被动语态，“memorization” 是主语，“required” 是过去分词作表语。

句子4：You can get to it from first principles.

• 结构：简单句。
• “get to” 是谓语动词短语；“it” 是宾语；“from first principles” 是介词短语作状语，“first principles” 意为“第一性原理”。

句子5：And every piece of what you know is like a Lego block that just fits in and forms a steel frame.

• 结构：复合句，包含主句和定语从句。
• 主句：“every piece of what you know is like a Lego block” 中，“what you know” 是宾语从句，作“of”的宾语；“is like” 是系表结构。
• 定语从句：“that just fits in and forms a steel frame” 由“that”引导，修饰“a Lego block”，“fits in” 和“forms” 是并列谓语。

句子6：It’s solid.

• 结构：简单句，主系表结构，“It” 是主语，“is” 是系动词，“solid” 是形容词作表语。