diff --git a/lib/errgonomic.rb b/lib/errgonomic.rb
index 4251eb3..27f253f 100644
--- a/lib/errgonomic.rb
+++ b/lib/errgonomic.rb
@@ -30,7 +30,9 @@ class NotPresentError < Error; end
   class TypeMismatchError < Error; end
 
   class UnwrapError < Error
-    def initialize(msg, value)
+    attr_reader :value
+
+    def initialize(msg, value = nil)
       super(msg)
       @value = value
     end
@@ -47,8 +49,9 @@ class NotComparableError < StandardError; end
   class SerializeError < TypeError; end
 
   # A little bit of control over how pedantic we are in our runtime type checks.
+  # Default is false: we are pedantic and raise errors on type mismatches.
   def self.give_me_ambiguous_downstream_errors?
-    @give_me_ambiguous_downstream_errors || true
+    !!@give_me_ambiguous_downstream_errors
   end
 
   # You can opt out of the pedantic runtime checks for lazy block evaluation,
diff --git a/lib/errgonomic/option.rb b/lib/errgonomic/option.rb
index eb76830..4b81bf6 100644
--- a/lib/errgonomic/option.rb
+++ b/lib/errgonomic/option.rb
@@ -257,7 +257,7 @@ def or_else(&block)
         return self if some?
 
         val = block.call
-        if !val.is_a?(Errgonomic::Option::Any) && Errgonomic.give_me_ambiguous_downstream_errors?
+        if !val.is_a?(Errgonomic::Option::Any) && !Errgonomic.give_me_ambiguous_downstream_errors?
           raise Errgonomic::ArgumentError.new, "block must return an Option, was #{val.class.name}"
         end
 
@@ -275,16 +275,17 @@ def and(other)
         other
       end
 
-      # If self is Some, call the given block and return its value. Block most return an Option.
+      # If self is Some, call the given block with the inner value and return
+      # its result. Block must return an Option.
       #
       # @example
-      #   None().and_then { Some(1) } # => None()
-      #   Some(2).and_then { Some(3) } # => Some(3)
+      #   None().and_then { |x| Some(x + 1) } # => None()
+      #   Some(2).and_then { |x| Some(x + 1) } # => Some(3)
       def and_then(&block)
         return self if none?
 
-        val = block.call
-        if Errgonomic.give_me_ambiguous_downstream_errors? && !val.is_a?(Errgonomic::Option::Any)
+        val = block.call(value)
+        if !Errgonomic.give_me_ambiguous_downstream_errors? && !val.is_a?(Errgonomic::Option::Any)
           raise Errgonomic::ArgumentError.new, "block must return an Option, was #{val.class.name}"
         end
 
diff --git a/lib/errgonomic/result.rb b/lib/errgonomic/result.rb
index 0478c2d..97df1e7 100644
--- a/lib/errgonomic/result.rb
+++ b/lib/errgonomic/result.rb
@@ -142,7 +142,7 @@ def and_then(&block)
         return self if err?
 
         res = block.call(value)
-        if !res.is_a?(Errgonomic::Result::Any) && Errgonomic.give_me_ambiguous_downstream_errors?
+        if !res.is_a?(Errgonomic::Result::Any) && !Errgonomic.give_me_ambiguous_downstream_errors?
           raise Errgonomic::ArgumentError, 'and_then block must return a Result'
         end
 
@@ -173,20 +173,18 @@ def or(other)
       # Sorry about that, hopefully it helps your tests. Better than ambiguous
       # downstream "undefined method" errors, probably.
       #
-      # TODO yield the Err
-      #
       # @param block [Proc]
       #
       # @example
-      #   Ok(1).or_else { Ok(2) } # => Ok(1)
-      #   Err(:o).or_else { Ok(1) } # => Ok(1)
-      #   Err(:q).or_else { Err(:r) } # => Err(:r)
-      #   Err(:s).or_else { "oops" } # => raise Errgonomic::ArgumentError, "or_else block must return a Result"
+      #   Ok(1).or_else { |e| Ok(2) } # => Ok(1)
+      #   Err(:o).or_else { |e| Ok(1) } # => Ok(1)
+      #   Err(:q).or_else { |e| Err(:r) } # => Err(:r)
+      #   Err(:s).or_else { |e| "oops" } # => raise Errgonomic::ArgumentError, "or_else block must return a Result"
       def or_else(&block)
         return self if ok?
 
-        res = block.call(self)
-        if !res.is_a?(Errgonomic::Result::Any) && Errgonomic.give_me_ambiguous_downstream_errors?
+        res = block.call(value)
+        if !res.is_a?(Errgonomic::Result::Any) && !Errgonomic.give_me_ambiguous_downstream_errors?
           raise Errgonomic::ArgumentError, 'or_else block must return a Result'
         end
 
@@ -249,8 +247,7 @@ def tap_ok(&block)
       def map(&block)
         return self if err?
 
-        @value = block.call(value)
-        self
+        Ok(block.call(value))
       end
 
       # Refuse to serialize an unwrapped Result as a String. Results must be