First, you need a summary field that will count the records in your found set. With correct sorting, this field will report the number of "won" and "lost" records.
Define a summary field in your table that "counts" another field in your table. Select a field that is never empty such as a serial ID field if you have one. We'll call this field, sCount for future reference here.
Second, set up your pie chart and specify sCount as your "value data". Select your field with "won" or "lost" as your label data.
Now be sure to specify the following two chart options:
Use data from current found set
Show data points from groups of records when sorted.
You can put this chart in the layout body and specify a form view as you only need one chart for the entire found set.
Enter browse mode and sort your records by the field with "won" or "lost" to group the data correctly and you should now get a pie chart with two "wedges" labled "won", "lost" with percentages for each.
If you've set up summary reports with sub summary parts before, you may notice a distinct similarity between the wedges of your chart and sub summary layout parts--both only show the correct subrtotals or percentages if the found set of records is correctly grouped by sorting.