How a Simple UI Oversight Almost Cost Millions: A Software Engineer's Deep Dive into Problem-Solving

Um, let me think. Uh, so, I have one time experience, but it's not like uh Oh, there is a problem that I need to deal with, is actually I find a a big problem in our inside our product that I raised it and then we later on solve this problem and then to prevent a, a huge loss. So what happened is, uh, when I was working on a financial product, um, We Ask our users to say how many percentage that they will contribute to their 401k based on their salary. Uh, on the UI screen, we make it as a percentage, but then in the backend service, we save it as a fixed amount, which makes sense if you are the first-time user, right? So let's say you are contribute, you, you are contributing 5% of your base salary, uh, $100,000. However, your salary, your base salary continue growing. But we're still saving the fixed amount as your contribution amount in our database. So after 1 or 2 years, it actually Mess up for our user. And I figured this issue out based on I just like throwing a whole bunch of user scenario with the XML uh test data. And then I saw the number doesn't look quite right to me. And I continue to dig deeper, and I realized that We are actually saving a fixed amount instead of the percentage percentage commotion based on the um updating salary. And I raised these issues to the director of PM and also the director of uh QA manager. And this actually caused our company a million dollars loss to pay off the user because over the past 10 years, the stock market going up and then they were supposed to invest $10,000 a year, but because of our system, they only invested $5000 a year. And However, because I catch this issue. It prevents us further loss. So, this is like how I handle a fake. Problem. I know that I'm not exactly answering your questions, but no, this

Yes. So, uh, because I enjoy like working on this products so much, so, uh, when I have spare time, I just like look into the logs, and then I also, we, we also have many XML test data plans because there are like Hundreds of 401k plans in the United States. So I occasionally test different data in order to see whether our UI handle enough edge cases. So while I was playing with those uh test, test data XML file, uh, and on the UI side, when I'm adding up the numbers, it doesn't look correct to me. So I continue uh calculate those number deeper, and I realized that The number calculation is wrong because some of them is like percentage, and some of them is fixed amount. So, from your, um, from our intuitive calculation, it may not like come showing the incorrect answers to you at first. But then if you think deeper, then you will see this 5% adding up like $10,000. Equals to $12,000 you need to actually like do the calculation by hand in order to figure out this error. And that's how I, how I figure out the error on our UI side. So I continue to look deeper and then try to uh work with, uh, work on this calculation with the QA manager because she is the person who Uh, mastering like how to do the calculation correctly on that particular scenario. And then we figure out that we actually have our calculation wrong, because the 5% conversion, we always keep it like behind the scene, it, we always keep the fixed amount instead of the real uh base salary.

so, so that's how I figure out the, the issue.

Uh, it's actually the The actual amount for um about like 30 users in our um In our company. Because like maybe just like one or two users, they, um, they may think they are being impacted, but then after we um figure out these issues, we have to reach out to our customers that this, uh, your potential loss over the stock market, uh, over the past couple of years if you invested like $10,000 instead of like $5000. Um, and that's why, uh, that's how we reach out to our customer and then uh send them the payoff based on uh the actual uh base salary amount and the contribution amount and also the S&P 500 index fund, uh. Rising point over the past couple of years.

Uh, so it's not like an internal tools, but then that platform isn't being, uh, Adopting by a whole bunch of new users, we have a classic, um, classic platform, and we also have the new platform. And then for the new platform, we have uh 30,000 users, I believe. But then, um, this kind of scenario will only happen to a. Particular uh 401k plans. And only if the particular 401k plan, they decide to use the percentage as their UI presenting instead of as the fixed amount as the UI presenting. So, uh, that's why we can narrow down the users into just by 30 instead of like thousands of users being impacted.