diff --git a/content/books/things-i-learnt/_index.md b/content/books/things-i-learnt/_index.md
index b7692ba..7eeb593 100644
--- a/content/books/things-i-learnt/_index.md
+++ b/content/books/things-i-learnt/_index.md
@@ -30,5 +30,6 @@ template = "section-contentless.html"
 		* [Beware of Interface Changes](interface-changes)
 		* [It's Better To Let The Application Crash Than Do Nothing](crash-it)
 		* [If You Know How To Handle It, Handle It](handle-it)
+		* [Types Say What You Data Is](data-types)
 * Community/Teams
 	* [A Language Is Much More Than A Language](languages-are-more)
diff --git a/content/books/things-i-learnt/data-types/index.md b/content/books/things-i-learnt/data-types/index.md
new file mode 100644
index 0000000..8994c85
--- /dev/null
+++ b/content/books/things-i-learnt/data-types/index.md
@@ -0,0 +1,40 @@
++++
+title = "Things I Learnt The Hard Way - Types Say What You Data Is"
+date = 2019-06-24
+
+[taxonomies]
+tags = ["en-au", "books", "things i learnt", "types"]
++++
+
+Memory is just a sequence of bytes; bytes are just numbers from 0 to 255; what
+those numbers mean is described on the language type system.
+
+<!-- more -->
+
+For example, in C, a `char` type of value 65 is most probably the letter "A",
+which an `int` of value is 65 is the number 65.
+
+Remember this when dealing with your data.
+
+And it doesn't matter of your language of choice uses dynamic typing or static
+typing. The same still applies.
+
+One classic example of misusing types is adding booleans. Booleans are either
+`true` or `false`, but because most languages follow C, which doesn't have a
+boolean type and uses compiler pre-processors to define `TRUE` as an integer
+with the value `1` and `FALSE` with another integer with the value `0`. And
+so, the build on top of what older developers knew, other languages use the
+same concepts. And so, you have a list of booleans and want to know how many
+true values are in the list, you can simply add them all.
+
+Let me point that again: You're adding booleans and expecting a number.
+
+No, you're counting the number of elements in the list 'cause that would see
+the whole list. You're not even filtering the false values over and counting
+the resulting list size. You're jumping the underlying type to get a bit of
+performance out.
+
+Fortunately, new languages are based on ML, which wouldn't allow this kind of
+stuff.
+
+{{ chapters(prev_chapter_link="/books/things-i-learnt/handle-it", prev_chapter_title="If You Know How To Handle It, Handle It", next_chapter_link="/books/things-i-learnt/languages-are-more", next_chapter_title="A Language Is Much More Than A Language") }}
diff --git a/content/books/things-i-learnt/handle-it/index.md b/content/books/things-i-learnt/handle-it/index.md
index 2bc74c5..87f7a25 100644
--- a/content/books/things-i-learnt/handle-it/index.md
+++ b/content/books/things-i-learnt/handle-it/index.md
@@ -27,4 +27,4 @@ occur, _deal with it_. If you have to save the save the content of the user
 somewhere else, log it to be reprocessed later or even just show an error
 message, do it.
 
-{{ chapters(prev_chapter_link="/books/things-i-learnt/crash-it", prev_chapter_title="It's Better To Let The Application Crash Than Do Nothing", next_chapter_link="/books/things-i-learnt/languages-are-more", next_chapter_title="A Language Is Much More Than A Language") }}
+{{ chapters(prev_chapter_link="/books/things-i-learnt/crash-it", prev_chapter_title="It's Better To Let The Application Crash Than Do Nothing", next_chapter_link="/books/things-i-learnt/data-types", next_chapter_title="Types Say What You Data Is") }}
diff --git a/content/books/things-i-learnt/languages-are-more/index.md b/content/books/things-i-learnt/languages-are-more/index.md
index 7559ef9..8a3404d 100644
--- a/content/books/things-i-learnt/languages-are-more/index.md
+++ b/content/books/things-i-learnt/languages-are-more/index.md
@@ -39,4 +39,4 @@ surface of what the whole of a language encapsulates and if you ignore the
 other elements in it, you may find yourself with a cute language in a
 community that is always fighting and never going forward.
 
-{{ chapters(prev_chapter_link="/books/things-i-learnt/handle-it", prev_chapter_title="If You Know How To Handle It, Handle It") }}
+{{ chapters(prev_chapter_link="/books/things-i-learnt/data-types", prev_chapter_title="Types Say What You Data Is") }}